1. Field of the Invention
The present invention relates to a detecting method for detecting internal state of a rechargeable battery and a detecting device suitable for practicing said detecting method. The internal state here is meant to include deterioration state, remaining capacity (=presently stored electricity quantity=dischargeable capacity), usable capacity (=presently residual electricity quantity which is still able to operate an instrument), charging capacity, electricity storable capacity, and internal resistance of said rechargeable battery. The present invention also relates an instrument provided with said detecting device. The present invention includes a program of detecting said internal state of said rechargeable battery and a medium having said program accommodated therein which are available in said detecting method and said detecting device.
2. Prior Art
In recent years, along with development of semiconductor elements and development of miniature, light-weight and high performance rechargeable batteries, mobile instruments such as portable personal computers, video cameras, digital cameras, cellular phones, and personal digital assistants including palmtop PCs have been rapidly progressed.
Separately, in recent years, the global warming of the earth because of the so-called greenhouse effect to an increase in the content of CO2 gas in the air has been predicted. For instance, in thermal electric power plants, thermal energy obtained by burning a fossil fuel is converted into electric energy, and along with burning of such fossil fuel, a large amount of CO2 gas is exhausted in the air. Accordingly, in order to suppress this situation, there is a tendency of prohibiting to newly establish a thermal electric power plant. Under these circumstances, so-called load leveling practice has been proposed in order to effectively utilize electric powers generated by power generators in thermal electric power plants or the like, wherein using a load conditioner having a rechargeable battery installed therein, a surplus power unused in the night is stored in rechargeable batteries installed at general houses and the power thus stored is used in the daytime when the demand for power is increased, whereby the power consumption is leveled.
Separately, in recent years, electric vehicles comprising a rechargeable battery and which do not exhaust any polluting substances have been proposed. Besides hybrid powered automobiles in which a combination of a rechargeable battery and an internal combustion engine or a fuel cell is used and the fuel efficiency is heightened while restraining exhaustion of polluting substances have been also proposed. As the rechargeable battery used in these electric vehicles and hybrid powered automobiles, a high performance rechargeable battery having a high energy density is expected to be developed.
Such rechargeable battery used in the mobile instrument, the load conditioner used for practicing the load leveling, the electric vehicle and the hybrid powered automobile typically includes a rechargeable lithium battery (including a lithium ion battery) in which reduction-oxidation reaction of lithium is used, a nickel-hydride rechargeable battery, a nickel-cadmium rechargeable battery, and a lead rechargeable battery.
Incidentally, in each of the mobile instrument, the load conditioner in the load leveling, the electric vehicle and the hybrid powered automobile, it is important to be able to precisely detect the dischargeable capacity (the remaining capacity), the usable capacity and the lifetime of the rechargeable battery in order to prevent the operation of the mobile instrument, the load conditioner, the electric vehicle or the hybrid powered automobile from being suddenly stopped.
In order to detect the usable capacity of a rechargeable battery, there is known a method wherein the voltage of the battery is measured and based on the measured result, the usable capacity is estimated.
The term xe2x80x9cremaining capacityxe2x80x9d of the rechargeable battery is meant a presently stored electricity quantity which can be discharged.
The term xe2x80x9cusable capacityxe2x80x9d is meant a presently residual electricity quantity of the rechargeable battery with which an instrument (or apparatus) having said rechargeable battery can be still operated. The usable capacity is included in the term remaining capacity.
Aforesaid method is applicable in the case of a lithium ion rechargeable battery whose anode material comprising a carbonous material difficult to convert into a graphite and which is distinguished from a graphite, because the battery voltage is gradually decreased in proportion to the quantity for the electricity to be discharged, and therefore, the presently residual electricity quantity can be detected by measuring the battery voltage. However, the method is not always applicable in other rechargeable batteries whose battery voltage is not gradually decreased in proportion to the quantity for the electricity to be discharged as in the case of the lithium ion rechargeable battery (whose anode comprising a graphite), where it is difficult to precisely detect the remaining capacity for the reason that the battery voltage is varied depending on the electric current flown and it is not proportional to the quantity for the electricity to be discharged. Besides, in the case of a rechargeable battery whose performance has been deteriorated to close its lifetime, it is extremely difficult to detect the remaining capacity. Separately, in the case of a lithium ion rechargeable battery whose anode material comprising a graphite series carbonous material, because the battery voltage with respect to the quantity for the electricity to be discharged is flat, the remaining capacity is difficult to obtain from the battery voltage in accordance with the foregoing method.
There is known other method in order to detect the remaining capacity of a rechargeable battery, wherein a cumulative discharged-electricity quantity is memorized and the cummulative discharged-electricity quantity is subtracted from a charged-electricity quantity to obtain a presently residual electricity quantity (that is, a remaining capacity). However, this method has such disadvantages as will be described in the following. That is, the current value and the discharge time are necessary to be always memorized. Besides, in the case where additional charging is performed for the rechargeable battery which is unknown with respect to the discharge depth, although the charged-electricity quantity at that time can be detected, the remaining capacity of the rechargeable battery after the rechargeable battery is subjected to charging cannot be precisely detected because the remaining capacity of the rechargeable battery before the additional charging is unknown. When the method is adopted in this case, because the method is to obtain a remaining capacity by comparing the cumulative discharged-electricity quantity with the remaining capacity prior to the discharging, a large error is likely to occur in the measurement.
Therefore, the method is difficult to cope with a rechargeable battery whose performance has been deteriorated to close its lifetime, where it is difficult to precisely detect the remaining capacity.
Now, Japanese Unexamined Patent Publication No. 2066/1992 discloses a method for observing the capacity of a lead battery in accordance with recovery characteristic of the battery voltage after pulse discharge. Japanese Unexamined Patent Publication No. 136774/1992 discloses a method wherein for a rechargeable battery, when the power source is ON, discharging is temporarily performed at a large current to detect a decrease in the battery voltage, the detected decrease value is compared with a prejudged battery voltage value, where when the difference is great, the residual capacity is judged to be insufficient. Japanese Unexamined Patent Publication No. 16607/1999 discloses a method wherein for a rechargeable battery, the battery voltage when a prescribed current is applied for a prescribed period of time is measured and the measured battery voltage is collated with a previously established battery voltage-residual capacity corresponding table to obtain a residual capacity of the battery. However, for a rechargeable battery whose performance has been deteriorated to increase the internal resistance or to decrease the battery capacity, any of these methods is difficult to precisely detect the residual battery capacity.
Separately, Japanese Unexamined Patent Publication No. 134742/1997 discloses a method wherein for a rechargeable battery, the internal impedance directly before reaching the discharge termination voltage is measured by an impedance-measuring instrument while flowing an alternate current to determine whether or not the rechargeable battery is deteriorated with respect its performance. However, this method is not practically applicable for the reason that such impedance-measuring instrument for measuring the impedance is required to have an alternate current-generating circuit and because of this, the apparatus involved unavoidably becomes large-sized, and in addition, during when the rechargeable battery is operated, the measurement cannot be performed.
Under these circumstances, there is an increased demand for providing a detecting method and a detecting device which enable one to precisely detect the presently residual electricity quantity for any rechargeable batteries even when they are such that their battery capacity is decreased or their internal resistance is increased and their performance is deteriorated. Besides, a detecting method and a detecting device which are applicable in any rechargeable batteries in order to precisely detect their lifetime, i.e., deterioration of their performance are expected to be developed.
The present invention is aimed at solving the shortcomings in the prior art in that in any of the proposed methods, the detection precision of the presently residual electricity quantity of the rechargeable battery is inferior.
Another object of the present invention is to provide a detecting method which enables one to detect the presently residual electricity quantity of any rechargeable battery at an improved precision even when the rechargeable battery is a rechargeable battery whose performance is deteriorated.
A further object of the present invention is to provide a detecting device which enables one to detect the presently residual electricity quantity of any rechargeable battery at an improved precision even when the rechargeable battery is a rechargeable battery whose performance is deteriorated.
A further object of the present invention is to provide an instrument provided with said detecting device.
A further object of the present invention is to provide a program of detecting internal state of said rechargeable battery and a medium having said program accommodated therein which are usable in said detecting method and said detecting device.
The term xe2x80x9cinternal statexe2x80x9d is meant to include deterioration state, remaining capacity (electricity storable capacity), usable capacity, and internal resistance of the rechargeable battery.
The present inventors conducted studies through experiments in order to find out a practically applicable detecting method capable of precisely detecting internal state of a given rechargeable battery, said internal state including the deterioration state, electricity storable capacity, remaining capacity, usable capacity, and internal resistance.
Particularly, the experiments studies were conducted in the following manner. First, examination is conducted of whether or not a rechargeable battery is normal or deteriorated with respect its performance. In the case where the rechargeable battery is found to have been deteriorated, prior to detecting the rechargeable battery, the deterioration mode is judged depending on the situation of the kind of the deterioration mode, the remaining capacity or the internal resistance is computed.
As a result, it was found that this manner is effective in precisely detecting the internal state of the rechargeable battery.
In a preferred embodiment of the present invention, for a number of normal rechargeable batteries, data of characteristics of these batteries are provided; based on said data, a judgment mode is established; for a given rechargeable battery to be examined, judgment is conducted of whether the battery is short-circuited, whether the internal resistance of the battery is increased, and whether the electricity storable capacity is decreased respectively with reference to previously established standard of judgment; thereafter, depending on the state of the battery (the shutdown state, the charging state, or the discharging state), the extent of deterioration of the battery is grasped, and the remaining capacity (the presently stored electricity quantity) of the battery is computed. Thus, it is possible to detect the internal state of the battery at a high precision.
Further, by equipping a battery module, an instrument or a machine with an apparatus designed so that a detecting method for detecting internal state of a rechargeable battery at a high precision according to the present invention can be function, it is possible to make the battery module or the instrument or machine in which a rechargeable battery is used as a power source to exhibit the performance to the full.
The detecting method according to the present invention comprises:
(i) a step in which a plurality of normal non-deteriorated rechargeable batteries are provided, these batteries are separately subjected to charging and discharging under various temperature conditions and at various rates of charge or discharge where their battery voltages, and their presently stored electricity quantities (their electricity quantities capable of being discharged) or their discharging capacities are obtained, and from these factors, basic data are obtained; and
(ii) a step in which for a rechargeable battery (ii-a) to be detected, the voltage value or/and the current value thereof are measured, and the measured result is compared with said basic data to judge:
(a) the rechargeable battery (ii-a) is short-circuited,
(b) the internal resistance of the rechargeable battery (ii-a) is increased,
(c) the electricity storable capacity (the quantity of electricity capable of being stored) of the rechargeable battery (ii-a) is decreased,
(d) the electricity storable capacity of the rechargeable battery (ii-a) is decreased and the internal resistance thereof is increased, or
(e) the rechargeable battery (ii-a) is not deteriorated (normal).
Here, the xe2x80x9cnormal rechargeable batteryxe2x80x9d means a rechargeable battery which can achieve a specification of performance such as a nominal capacity or the like of a product (a rechargeable battery).
The xe2x80x9celectricity storable capacityxe2x80x9d is meant the quantity of electricity capable of being stored in a rechargeable battery, which is corresponding to a nominal capacity as a product. In other words, the presently stored electricity quantity (that is, the remaining capacity) indicates the quantity of electricity capable of being discharged from the then state thereof.
In the present invention, judgment of a combination of two or more of the foregoing items (a) to (e) is also included.
The above-described basic data includes the following factors.
(1) For a normal rechargeable battery having a given open-circuit voltage (Voc). The remaining capacity (Q) [the presently stored electricity quantity] of the battery to the open-circuit voltage (Voc) is measured.
Data or function formula of the relationship with respect to Voc(Q) or Q(Voc) of the open-circuit voltage (Voc) of the battery to the remaining capacity (Q) [the presently stored electricity quantity]. The function Voc(Q) is an open-circuit voltage function formula as a function of the remaining capacity (Q). The function Q(Voc) is a function formula of the remaining capacity (Q) as a function of the open-circuit voltage (Voc).
(2) For a normal rechargeable battery in a full charged state, battery voltages Vd are measured under various temperature conditions T and at various discharge rates Id. The charging is tentatively suspended, where the open-circuit voltage (Voc) is measured. Data or function formula Vd(Voc, Id, T) of the relationship of the battery voltages Vd to the Id, Voc and T. Or the data or function formula Vd(Q, Id, T) or Q(Vd, Id, T) computed from the data or function formula of the relationship of the Voc(Q) of the open-circuit voltage (Voc) to the remaining capacity (Q) described in the above (1).
(3) In the above (2), when the internal resistance of the battery is made to be Rd, there is established relation expression Vd=Vocxe2x88x92Idxc3x97Rd or Rd=(Vocxe2x88x92Vd)/Id.
Data computed from this relation expression or function formula Rd(Voc, Id, T) or Rd(Vd, Id, T) obtained based on the data. Or the data or function formula Rd(Q, Id, T) or Q(Rd, Id, T) of the internal resistance (Rd), obtained from the data or function formula of the relationship with respect to Voc(Q) of the open-circuit voltage (Voc) to the remaining capacity (Q) in the above (1).
(4) For a normal rechargeable battery with no electricity stored therein maintained under temperature condition T, the rechargeable battery is subjected to charging at a charge rate (Ic), where the battery voltage (Vc) is measured, and the charging is tentatively suspended, where the open-circuit voltage (Voc) is measured.
Data or function formula Vc(Voc, Ic, T) of the relationship of the battery voltage (Vc), the open-circuit voltage (Voc), and the charge rate (Ic). Or data or function formula Vc(Q, Ic, T) or Q(Vc, Ic, T) of the battery voltage (Vc), computed from the data or function formula Voc(Q) with respect to the open-circuit voltage (Voc) to the remaining capacity (Q) in the above (1).
(5) In the above (4), when the internal resistance of the battery is made to be Rc, there is established relation expression Vc=Voc+Icxc3x97Rc or Rc=(Vcxe2x88x92Voc)/Ic.
Data computed from this relation expression or function formula Rc(Voc, Ic, T) obtained based on the data. Or data or function formula Rc(Q, Ic, T) or Q(Rc, Ic, T) of the internal resistance (Rc), obtained from the data or function formula of the relationship with respect to Voc(Q) of the open-circuit voltage (Voc) to the remaining capacity (Q) in the above (1).
The foregoing basic data comprises at least data or a function formula selected from the above (1) to (5).
According to the detecting method for detecting internal state of a rechargeable battery in the present invention, on the basis of the foregoing basic data or function formulas and in accordance with a prescribed judgment mode while referring to information selected from the open-circuit voltage, battery voltage and internal resistance of a rechargeable battery to be detected in a shutdown state, a charging state, or a discharging state, it is possible to precisely detect the internal state of rechargeable battery.
In the present invention, it is assumed that the transient battery voltage when the charge rate or the discharge rate is changed can be expressed by an exponential function exe2x88x92t/xcfx84 (with e being the base of the natural constant, t being a time, and xcfx84 being a time constant which is decided by the impedance or the like of the battery), and based on the function, the internal resistance, an increase ratio of the internal resistance, and a decrease ratio of the electricity storable capacity are computed, whereby the remaining capacity (the dischargeable capacity) can be obtained.
Further, in the detecting method of the present invention, by computing the remaining capacity which is reached to the minimum voltage (the lowest operating voltage) required in order to operate an equipment in which a rechargeable battery is used as a power source and referring to the consumed current or the consumed power of the equipment, it is possible to find out the residual operating time of the equipment. By this, it is possible that sudden stoppage of the operation of the equipment is avoided in advance and at a suitable occasion, replacement of the rechargeable battery by a new rechargeable battery or charging for the rechargeable battery is performed.
Thus, the present invention provides a detecting method and a detecting device which enable one to detect internal state of a rechargeable battery at a high precision. According to the present invention, it is possible to readily control a power source of an equipment or an apparatus in which the rechargeable battery is used as the power source. In addition, it is possible to readily find out the residual operating time of the equipment or apparatus, the timing required to charge the power source, and the timing required to replace the rechargeable battery by a new rechargeable battery. Further, by adding the detecting device of the present invention to a battery module, a charger, an equipment or a apparatus in which a rechargeable battery is used as a power source, it is possible that the performance of the rechargeable battery as the power source is exhibited to the utmost limit. In addition, it is possible to make the equipment or apparatus to efficiently operate so as to maximize the function. Further, by adding the detecting device of the present invention to an inspection equipment to determine whether a rechargeable battery product is good or not good prior to shipping, shipment inspection for a rechargeable battery product can be performed at a high precision.
According to the present invention, the energy which a rechargeable battery possesses can be used to the full, and it makes it possible to desirably prolong the operating time of an instrument in which a rechargeable battery is used as the power source.